The present invention relates to a chain shifting assembly for bicycles wherein the chain is moved in a parabola track to smoothly engage with the sprockets of derailleur.
A conventional chain shifting assembly for bicycles is shown in FIG. 6 and generally includes a four-link mechanism which includes a first link xe2x80x9cAxe2x80x9d which is connected to the bicycle frame by part xe2x80x9cA1xe2x80x9d, a second link xe2x80x9cBxe2x80x9d which is pivotally connected to the first link xe2x80x9cAxe2x80x9d, a third link xe2x80x9cCxe2x80x9d which is pivotally connected to the second link xe2x80x9cBxe2x80x9d, and a fourth link xe2x80x9cDxe2x80x9d which is pivotally connected between the first link xe2x80x9cAxe2x80x9d and the third link xe2x80x9cCxe2x80x9d. A derailleur cable 5 is fixed connected to the second link xe2x80x9cBxe2x80x9d and the other end of the cable 5 is connected to a shifter on the handlebar (both not shown) of the bicycle. A shift frame xe2x80x9cC1xe2x80x9d is connected to the third link xe2x80x9cCxe2x80x9d and is able to shift the chain 7 to engage with one of the sprockets 6 of the derailleur.
As shown in FIG. 7, when pulling the cable 5 by operating the shifter, the four-link mechanism is activated to move the shift frame xe2x80x9cC1xe2x80x9d to move the chain 7 from a small sprocket to a large sprocket. It is to be noted that, as shown in FIG. 8, the track that the chain 7 moves is basically on a horizontal plane and this horizontal movement can not make the chain 7 to smoothly change from the smaller sprocket to the larger sprocket. Therefore, the chain 7 could not well engage with the target sprocket and/or there will be a large friction between the sprockets 6 and the chain 7. Besides, this type of four-link mechanism is only used for the shifter on the handlebar. It needs another type of mechanism if the shifter is connected to the bicycle frame at a lower position.
In accordance with one aspect of the present invention, there is provided a chain shifting assembly for bicycles and the assembly comprises a fixed member fixed to a bicycle frame and an operation member is pivotally connected to the fixed member and includes a first arm, a second arm and a third arm. A derailleur cable is fixed to the second arm and a shifting member is pivotally connected to the first arm. A shift frame is connected to the other end of the shifting member. An angle limitation member is pivotally connected to the fixed member and the shifting member respectively. A spring is connected between the fixed member and the angle limitation member.
The primary object of the present invention is to provide a bicycle chain shifting assembly whose chain shift frame is moved along a parabola-shaped track.
Another object of the present invention is to provide a bicycle chain shifting assembly wherein the assembly can be used with the shifter located on the handlebar or the bicycle frame.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.